The invention relates to a torsional vibration damper with variable resonance frequency.
Components in machines and equipment including, in particular, rotating components, can be excited into undesirable torsional vibration through periodic pulsating torques. These torsional vibrations, which are superimposed on the desired uniform rotary motion, can interfere with the synchronous running of groups of units and can lead to excessive stresses, particularly in the resonance ranges.
It is already known in the art to limit harmful torsional vibrations by means of torsional vibration dampers. These torsional vibration dampers are adjusted in such a way that they dampen excitation torques with a specific frequency. If the excitation torques occurring in the machines or the equipment have a frequency that is proportional to the variable operating speed of the components, the frequency of the torsional vibration damper is adjusted to a resonance point with a particularly high load. The torsional vibration damper is then not effective at other operating speeds. Such a torsional vibration damper is described, for instance, in DE 43 35 766 A1.
For machines and equipment with variable rotational speed, it is desirable, however, to achieve damping of the excitation torques over the entire rotational speed range. In this connection, DE 196 31 989 has already described the use of pendulum oscillators. Such pendulum oscillators consist, for instance, of rollers or oscillating rings that move in orbits inside hollow cylinders. These solutions have the drawback, however, that an effective embodiment requires a significant size, which substantially limits their applicability.
DE 196 41 763 discloses a straight-motion vibration damper in which an inertial mass is fixedly connected with a free end of a leaf spring, for which an adjustable support element is provided to change the effective length of the leaf spring and thereby to make the resonance frequency of the vibration damper adjustable. Here, the support is adjusted by means of a control unit with a sensor for detecting the excitation frequency and an electric motor. This is a comparatively complex electrical solution. Moreover, the vibration damper is not suitable for use as a torsional vibration damper.
Furthermore, DE Patent 632 057 discloses a torsional vibration damper, which has a support plate mounted to a rotating shaft on which a flexural spring arrangement is disposed and guided radially outwardly to an inertial mass. The inner end of the flexural spring arrangement is fixed by clamping. Supports constructed as slide elements, which are arranged in radial guides of the support plate and execute a back and forth movement during each rotation, are provided on the flexural spring arrangement. Through the position of these slide elements, the natural frequency of the connection between the rotating shaft and the inertial mass is changed in a continuously varying and periodic manner in the course of each rotation. As a result the shaft never runs with natural frequencies that harmonize with its own rotational speed for more than very short periods. However, this continuous variation of the natural frequency only achieves that the torsional vibrations of a shaft cannot reach their full amplitude.
The object of the invention is to provide a torsional vibration damper with a simple structure that makes it possible to dampen excitation torques over the entire rotational speed range.
This object according to the invention is attained by the invention as described and claimed hereinafter. Preferred embodiments also are set forth.
The invention provides that the torsional vibration damper has a support plate fixed to a rotating shaft on which is disposed a flexural spring arrangement guided radially outwardly to an inertial mass and the inner end of the flexural spring arrangement is fixed by clamping. On the flexural spring arrangement a support is provided, which is constructed as at least one slide element arranged in a radial guide element of the support plate. A restoring force of a restoring spring, which acts in a direction opposite the centrifugal force that results from a rotational movement, is applied to the slide element. The slide element, under the influence of the centrifugal force and the restoring force, can be radially moved in the guiding element. Means are provided with which the restoring force acting in the direction opposite the centrifugal force can be changed as a function of the speed of rotation in such a way that the resonance frequency of the torsional vibration damper can be automatically adjusted to the rotational speed by the position of the slide element.
According to a preferred embodiment of the invention, the means with which the restoring force acting in the direction opposite the centrifugal force can be changed as a function of the speed of rotation are provided between the restoring spring and the at least one slide element. Consequently, based on the respectively acting centrifugal force, the magnitude of which depends on the centrifugal radius and the rotational speed, the slide element assumes a respective position on the flexural spring. This results in an effective length of the flexural spring, which defines a resonance of the torsional vibration damper required for a given rotational speed.
In the context of the invention, it is further provided that the flexural spring arrangement may comprise two opposite flexural springs extending radially outwardly from the support plate to the inertial mass, each with a slide element arranged in its radial guide element. This results in a balanced, simple construction of the torsional vibration damper.
It is furthermore provided that the slide elements can be arranged with a support guide on the flexural springs in a manner such that they span the springs and can slide along them, and that the flexural springs can be constructed as leaf springs.
Preferably, the means for rotational speed-dependent intensification of the restoring force of the restoring spring is provided with a tie member. The tie member extends to at least one slide element from a free base point of the restoring spring which can be displaced in a spring guide element perpendicularly to the guide element of the slide elements. In the rest position or at low rotational speeds, the tie member engages with the free end of the restoring spring at an acute angle and with the slide element at an obtuse angle, and with increasing speed of rotation it engages with the free end of the restoring spring at an increasingly larger angle and with the slide element at an increasingly smaller angle, such that the restoring force acting in opposite direction of the centrifugal force can be automatically changed as a function of the speed of rotation, and the slide element assumes a respective position on the flexural spring, from which results a resonance frequency corresponding to the rotational speed.
It may also be provided that both base points of the restoring spring constructed as a compression spring are displaceably guided in two spring guide elements extending perpendicularly to the guide element of the slide elements and that the base points are connected with the slide elements via two tie members each.
Preferably, the restoring spring furthermore has a linear characteristic and is constructed as a helical spring.
According to another embodiment of the invention, it may be provided that the means for the rotational speed-dependent intensification of the restoring force is a tie member mounted to the slide element. This tie member is extended to a cam plate, which is operatively connected with a restoring spring constructed as a spiral spring, such that the restoring force acting on the slide elements is intensified with increasing speed of rotation as a function of the rotation angle of the cam plate. In this case, the tie member is preferably guided to the slide element in a deflected manner via a deflecting sheave in the motion direction of the slide element.
It may be advantageous if two restoring springs, each with a slide element, are arranged opposite one another and a tie member extending to a cam plate is associated with each slide element.